All are good possibilities however my first guess is also the clutch basket is making the noise.A stock basket uses rivets to keep the gear and basket meshed together,there is actually a small gasket and cushions inbetween those rivets and basket.They have slight movement in that spot on all stock baskets.I would say take the basket off and see if it still does it??If it does than it wouldn't be the first counter balancer/bearing that I have seen blow out.Now get to wrenching cause you know we all want to know the answer to the noober mystery.lol